1. Field of the Invention
An apparatus for applying electromagnetic radiation to a surface such as the surface of a moving sheet of material by directing electromagnetic radiation towards a cylindrical roller which rolls on the surface and collecting and detecting electromagnetic radiation emerging from the roller.
2. Discussion of Prior Art
The present invention is directed to in-line or real-time process monitoring technology. More particularly to the problem of real-time spectroscopic determination of degree of chemical and physical changes to materials, in particular sheet materials, on a moving fabrication line. In many continuous-feed manufacturing processes involving sheet materials, monitoring the degree of chemical reaction and desiccation is essential and often problematic. Remote sensoring is often not possible due to the speed of material flow, or the necessity for sensor-element/sample contact. Many prior attempts to commercialize real-time monitoring systems have performed marginally or were useful under only a narrow range of circumstances. Most in-line spectroscopic methods are applicable to liquids where a flowing liquid sample moves through a light beam confined to a narrow and well defined optical cell which has been engineered to sit stationary within the flowing medium (Sting, D. W. Multiple Internal Reflection Cell Optical System for use in Infrared Spectroscopy for Liquid and Fluidized samples; Sting, D. W., Ed.; Sting, D. W.: USA, (1983) and (Milosevic, M. Multiple Internal Reflection Liquid Sampling; Milosevic, M., Ed.: USA). There are few instrumental methods which address the real-time infrared (or other wavelength range) spectroscopic determination of a moving solid sample. There are few optical arrangements which lend themselves to moving samples, most of them being non-contact in nature. Transmission infrared (or other) spectroscopy can be used only in cases where the sample is thin enough and non-absorbing enough so that the total absorption is not significantly greater than 1 (A=xe2x88x92log l/lo). At this point the linear relationship between peak attenuation and bond species concentration (Beer-Lambert law) no longer holds. Only extremely thin free-standing polymer films would be measurable by this transmission method. A great many sheet products would be too thick and too absorbing to be measurable by this technique. Another non-contact method is direct reflection from the moving sheet material. There are two variations on this: specular (mirror-like) and diffuse reflection. In the first, a beam of infrared (or other) light is impinged at an angle to the sheet, the light interacts with the sample and reflects. The reflected beam is directed to the detector. The first problem with this technique is that few materials are smooth enough to reflect in a specular way. Further, in the case of infrared spectroscopy very little light is generally reflected due to strong absorption of an infrared beam by most organic substances. For both reasons, too little light is reflected to enable a spectroscopic measurement of high enough quality for quantitative determination of bond concentrations.
In the case of sample types which are too rough to allow specular reflection (most samples), the light is reflected in a diffuse and scattered manner further burdening the collection of adequate reflected light to enable spectroscopic determination of the sample state. In this case a collection of concave mirrors are assembled to try to collect and recolumnate the scattered light; but rarely is the quality of the spectrum adequate for quantitative purposes.
Cylindrical cell types for multiple internal reflection have been used primarily for liquid analysis (Doyle, W., M., Internal Reflection Apparatus and Method Using Cylindrical Elements, (1989)). Diamond has been used for MIR spectroscopy (Sting, D.; Reffner, J. Radiant Energy Spectroscopy with Diamond Internal Reflection Element; Sting, D.; Reffner, J., Ed., (1993)), but not in thin film form. MIR has also been used in process monitoring applications (Stevenson, W. A. Monitoring Technology; Stevenson, W. A., Ed., (1987)). Several other uses for multiple internal reflection are known (Harrick, N. J., Multiple Internal Reflection, 3rd ed., John Wiley and Sons, (1967, 1987)).
No prior art examined has identified the use of MIR spectroscopy for moving sheet samples using cylindrical elements made or allowed to rotate with the sample, as described herein.